1. Field of the Invention
The present general inventive concept relates to a piezoelectric inkjet printhead, and more particularly, to a piezoelectric inkjet printhead that minimizes deviation of ink ejection performance caused by cross-talk.
2. Description of the Related Art
Generally, inkjet printheads are devices for printing a color image on a printing medium by ejecting droplets of ink onto a desired region of the printing medium. Depending on an ink ejecting method, inkjet printheads can be classified into two types: a thermal inkjet printhead and a piezoelectric inkjet printhead. The thermal inkjet printhead generates bubbles in ink to be ejected by using heat and ejects the ink utilizing an expansion of the bubbles, and the piezoelectric inkjet printhead ejects ink using a pressure generated by a deformation of a piezoelectric material.
FIG. 1 illustrates a general structure of a conventional piezoelectric inkjet printhead. Referring to FIG. 1, a manifold 2, a plurality of restrictors 3, a plurality of pressure chambers 4, and a plurality of nozzles 5 are formed in a flow channel plate 1 to form an ink flow channel. A piezoelectric actuator 6 is formed on a top area of the flow channel plate 1. The manifold 2 allows an inflow of ink from an ink tank (not illustrated), and the pressure chambers 4 are arranged along one side or both sides of the manifold 2 to store ink to be ejected. Each of the pressure chambers 4 is deformed by an operation of the piezoelectric actuator 6, such that ink can flow into or out of the pressure chamber 4 according to a pressure variation in the pressure chamber 4 caused by the operation of the piezoelectric actuator 6. The plurality of restrictors 3 connects the manifold 2 to corresponding ones of the plurality of pressure chambers 4.
Generally, the flow channel plate 1 is formed by individually manufacturing a silicon substrate and a plurality of thin metal or synthetic resin plates and by stacking the thin plates to form the ink channel portion. The piezoelectric actuator 6 is formed on top of the flow channel plate 1 above the pressure chamber 4 and includes a piezoelectric layer and an electrode stacked on the piezoelectric layer to apply a voltage to the piezoelectric layer. Therefore, a portion of the flow channel plate 1 forming an upper wall of the pressure chamber 4 functions as a vibrating portion 1a that is deformed by the piezoelectric actuator 6.
An operation of the conventional piezoelectric inkjet printhead will now be described. When the vibrating portion 1a (i.e., the portion of the upper wall of the pressure chamber 4 that functions as a vibrating portion 1a) is bent downward by the operation of the piezoelectric actuator 6, a volume of the pressure chamber 4 reduces, which increases a pressure inside the pressure chamber 4. Thus, ink is ejected from the pressure chamber 4 to outside of the printhead through the nozzle 5. When the vibrating plate 1a returns to its original shape according to the operation of the piezoelectric actuator 6, the volume of the pressure chamber 4 increases, which reduces the pressure of the pressure chamber 4. Thus, ink flows into the pressure chamber 4 from the manifold 2 through the restrictor 3.
However, in the conventional piezoelectric inkjet printhead, the pressure variation inside the pressure chamber 4 caused by the piezoelectric actuator 6 is also transmitted to neighboring pressure chambers 4. This phenomenon is called “cross-talk.” The cross-talk causes deviations in a speed and volume of ink droplets ejected through the plurality of nozzles 5.
FIG. 2A is a graph illustrating an ink droplet ejecting speed with respect to nozzle position when the plurality of nozzles 5 are simultaneously operated in a conventional piezoelectric inkjet printhead, and FIG. 2B is a graph illustrating an ink droplet ejecting speed with respect to nozzle position when only nozzles disposed in region A of FIG. 2A are simultaneously operated in the conventional piezoelectric inkjet printhead.
For example, in a conventional piezoelectric inkjet printhead for forming a color filter, a plurality of nozzles is operated at the same time. In this case, as illustrates in FIG. 2A, the speed of ink droplets ejected through nozzles disposed at both sides of the printhead is lower than that of ink droplets ejected through nozzles disposed at a center portion of the printhead.
Referring to FIG. 2B, nozzles disposed at the center portion of the printhead (i.e., only the nozzles in the region A of FIG. 2A) are simultaneously operated, whereas the low-speed nozzles disposed at both sides of the printhead are not operated. In this case, the speed of the ink droplets ejected through the nozzles is also lower at both sides of the region A of the printhead than in the center portion of the region A of the printhead.
From the graphs illustrates in FIGS. 2A and 2B, it can be seen that the deviation of the ink ejecting speed is not caused by a non-uniform manufacturing of the nozzles between the center portion and the side portions of the printhead. Specifically, when the side portion nozzles are not operated, a deviation of the ink ejecting speed occurs between the center-most nozzles of the center portion and the outer-most nozzles of the center portion. However, this deviation is minimized or absent when the side portion nozzles are operated along with the center portion nozzles (although a deviation of the ink ejecting speed occurs between the side portion nozzles and the center portion nozzles, as discussed above).
An ink ejecting speed of a conventional piezoelectric inkjet print head can vary with respect to a nozzle position for a various reasons, including the following.
When a pressure of each pressure chamber increases by an operation of the piezoelectric actuator, ink inside the pressure chamber is ejected through a nozzle, and at the same time some of the ink is pushed in a reverse direction to the manifold through the restrictor. The reverse flow of the ink via the manifold influences neighboring pressure chambers, thereby increasing a pressure of the neighboring pressure chambers. In this case, pressure chambers disposed in a center portion of the printhead are affected by the reverse flow of the ink in pressure chambers on both sides thereof. However, the pressure chambers disposed at both sides of the printhead are affected by the reverse flow of the ink from one side thereof. Therefore, an ink ejecting pressure of the pressure chambers at both sides of the printhead is lower than that of the pressure chambers at the center portion of the printhead.
In the conventional inkjet printhead, a vibrating portion of pressure chambers is formed in one piece (i.e., there is no separate vibrating plate attached to the pressure chambers). Therefore, when one piezoelectric actuators vibrates, neighboring pressure chambers are affected by the vibration of the piezoelectric actuator through the vibrating portion. In this case, pressure chambers disposed in the center portion of the printhead are affected by vibrations from both sides thereof, and pressure chambers disposed at both sides of the printhead are affected by vibrations from one side thereof. Therefore, the ink ejecting pressure of the pressure chambers is lower at both sides of the printhead than at the center portion of the printhead.
As described above, in the conventional piezoelectric inkjet printhead, an ink ejecting performance of a plurality of nozzles varies due to cross-talk, thereby changing the speed and volume of ejecting ink droplets.